This invention pertains to a key-actuated parking brake engagement/disengagement control for air brake equipped vehicles.
Air brake equipped vehicles such as trucks and buses normally utilize spring-type parking brakes. Air pressure is applied to disengage a spring mechanism in order to disengage the parking brakes. When the air pressure is relieved, the spring mechanism engages the parking brakes, which remain engaged until the air pressure is reapplied. A control valve allows the vehicle driver to exhaust air from the parking brake pneumatic circuit to engage the parking brakes; and, to repressurize the circuit in order to disengage the parking brakes.
There have been instances in which drivers have forgotten to actuate the parking brake control valve before leaving the vehicle. If the control valve is not properly actuated, the parking brakes are not engaged. There have been xe2x80x9croll awayxe2x80x9d incidents in which driverless buses have caused serious injuries while rolling away from a parked position, due to driver failure to operate the control valve so as to engage the parking brakes.
Although most trucks are equipped with a key-operated ignition switch, this is not universally true of buses. Many buses have an ignition switch which can be operated without a key. This invention provides a key-operated device which controls the vehicle parking brake (pneumatic) circuit to reduce the potential for vehicle xe2x80x9croll awayxe2x80x9d due to driver failure to engage the parking brakes.
The invention provides a vehicle brake lockout device for coupling between a pneumatically-operable vehicle parking brake and a pneumatic control valve. The control valve has a plunger which the vehicle driver can move between a brake-disengaging position in which pressurized air flows from a pressurized air supply through the control valve to the parking brake, and a brake-engaging position in which such air flow is prevented. In one embodiment, the device incorporates a shaft which can be rotated with respect to the plunger. The shaft has recessed and non-recessed portions. The plunger has a second recess. A key can be removably coupled to the shaft and rotated between engaged and disengaged positions. If the plunger is in the brake-engaging position then the key can be moved into the key""s engaged position. This causes the non-recessed portion of the shaft to protrude into the plunger""s recess, preventing movement of the plunger into the brake-disengaging position. In the key""s disengaged position, the recessed portion of the shaft intersects the plunger""s recess, permitting movement of the plunger between the brake-disengaging and engaging positions.
An optional switch can be coupled to the shaft such that the switch has a first electrical conductivity state when the key is in its engaged position and a second electrical conductivity state when the key is in its disengaged position. These switch states can be used for any desired purpose, such as controlling the vehicle""s ignition circuit. A second recessed portion on the shaft can be positioned adjacent the switch such that the switch is actuated into its first electrical conductivity state when the shaft""s second recessed portion is rotated into contact with the switch; with the switch being actuated into its second electrical conductivity state when the shaft""s second recessed portion is rotated away from contact with the switch.
An optional solenoid can be electrically connected to the vehicle""s ignition circuit. The solenoid has one operating state when the ignition circuit is energized and a second operating state when the ignition circuit is de-energized. The solenoid has a plug which is projected into or withdrawn from the plunger""s recess, depending on the solenoid""s operating state.